*3.1. Experimental Materials*

To study the overall pattern of carbon flux and consider the contingency of the experiment, three alloy steel materials were selected for carburization: 12Cr2Ni4A, 16Cr3NiWMoVNbE, and 18Cr2Ni4WA. Table 1 shows the chemical composition of the studied alloy steels. These materials enable the study of carbon flux values with different initial carbon contents and different alloying elements under different carburizing conditions. For this experiment, the samples were processed to have an outer diameter of 24 mm, a small hole with a diameter of 3 mm, and a thickness of 3 mm. As the mass increment is calculated in milligrams, the samples were specially cleaned to maintain the validity of the experiment. The vacuum furnace had a degreasing effect. The samples were first cleaned with alcohol and then dried, followed by heating in a vacuum furnace to 920 ◦C. They were kept warm for 30 min and then left to cool in the vacuum cooling chamber. The samples were weighed before and after carburization using a LE204E 1/10000 scale (Dongbo Thermal Technology Co., Ltd., Shenyang, China), and the average of the three experiments was considered the measurement value. The experiments were carried out in a dual-chamber vacuum carburizing furnace.

**Table 1.** Chemical compositions of the alloy steels (wt.%).

